Description

generic
   type Config_Data is limited private;
   -- The parameters read from the command line will be written in
   -- a variable of this type

   -- Set this to False if you want case insensitive option matching.
   -- For example, if you set this to False, "input", "Input", "INPUT"
   -- and "InPuT" will be equivalent names for the option "input"
   Case_Sensitive : Boolean := True;
package Generic_Line_Parser is

This is a generic package implementing a simple-to-use command line parser. Yes, I know, everyone makes his/her own command line parser... so, I wrote mine. As they say, every open source project starts with a programmer that schratches hes own itch. So I did... If you find this useful, you are welcome to use it.

The ideas behind this package are the following

* Parameters are nominal, non positional. The syntax is of "named parameter" type, that is, each command line parameter is expected to have thefollowing format

label ['=' value]

where "label" is any string without '='.

* Parsed value are written in a "configuration variable" whose type is a formal parameter of this package. The values are written in the configuration variable by using some callbacks provided by caller.

The names of the parameters are given to the parser in "parameter description array" that is an array of records that specify

+ The parameter name

+ A default value (if needed)

+ If the parameter is mandatory

+ If it can be specified more than once

+ The callback function to be called when the parameter is found

In order to parse the command line it suffices to call Parse_Command_Line giving as argument the array of parameter descriptors and the configuration variable to be written. For every parameter found, the corresponding callback function is called. If at the end of the parsing there are some optional parameters that were missing from the command line, the corresponding callbacks are called with the default parameter.

Types

Parameter_Callback - Spec

type Parameter_Callback is
     access procedure (Name   : in     Unbounded_String;
                       Value  : in     Unbounded_String;
                       Result : in out Config_Data);

Parameter_Descriptor - Spec

type Parameter_Descriptor is
      record
         Name      : Unbounded_String;    -- Parameter name
         Default   : Unbounded_String;    -- Default value used if not on C.L.
         Mandatory : Boolean;             -- Parameter MUST be given
         Only_Once : Boolean;             -- Parameter MUST NOT be given more than once
         Callback  : Parameter_Callback;  -- Called when parameter found
      end record;

Record holding the description of a parameter. The fields should be self-explenatory (I hope). The only field that needs some explanation is Name since it allows to specify more than one name for each parameter. The syntax is very simple: just separate the names with commas. For example, if Name is "f,filename,input" one can use on the command line, with the same effect f=/tmp/a.txt or filename=/tmp/a.txt or input=/tmp/a.txt. Spaces at both ends of the label name are trimmed, so that, for example, "f,filename,input" is equivalent to "f , filename ,input "

Parameter_Descriptor_Array - Spec

type Parameter_Descriptor_Array is
     array (Natural range <>) of Parameter_Descriptor;

Constants & Global variables

Bad_Command - Spec

Bad_Command : exception;

Subprograms & Entries

Parse_Command_Line - Spec

procedure Parse_Command_Line     ( Parameters : in     Parameter_Descriptor_Array;
Result :    out Config_Data;
Help_Line : in     String := "";
Help_Output : in     Ada.Text_IO.File_Type := Ada.Text_IO.Standard_Error);

Main exported method. It parses the command line and it writes the result in Result. If some error is encountered, Bad_Command is raised with an explicative exception message. Help_Line, if not empty, is written to Help_Output in case of error.

To_Float - Spec

function To_Float ( X : Unbounded_String)
return Float;

Convenient conversion function to Float that raise Bad_Command if the argument has not a valid syntax

To_Natural - Spec

function To_Natural ( X : Unbounded_String)
return Natural;